Problem: In chemistry class, the girl to boy ratio is $7$ to $7$. If there are a total of $28$ students, how many girls are there?
Explanation: A ratio of $7$ girls to $7$ boys means that a set of $14$ students will have $7$ girls and $7$ boys. A class of $28$ students has $2$ sets of $14$ students. Because we know that there are $7$ girls in each set of $14$ students, the class must have $2$ groups of $7$ girls each. There is a total of $14$ girls in chemistry class.